Genetic alterations that maintain cells in a poorly differentiated state are a hallmark of many leukemia and childhood cancers. Among them, neural crest-derived neuroblastoma is the most prevalent cancer in infants and the most common extracranial solid tumor in children with the majority of patients being 5 years old or younger. Approximately 650 neuroblastoma tumors of the sympathetic nervous system are diagnosed each year in the United States and 10,000 children a year worldwide. Although successfully managed in its milder forms, the 5-year survival rate for patients with high risk neuroblastoma under an aggressive therapeutic regimen is only 40% and is associated with a high morbidity. Safer and more effective treatments are needed to manage this condition. HaRo Pharmaceuticals, Inc. is developing a promising polypharmacological agent that affects two distinct but functionally interconnected cellular pathways, which have been shown to be important for the treatment of neuroblastoma. HR-770 is a bifunctional molecule that simultaneously inhibits histone deacetylases and activates retinoic acid receptors. Early evidence suggests that the unique mode of action (MOA) of this molecule may result in a safer and more effective cancer treatment due to the synergy between these two pathways. The purpose of this proposal is to optimize the in vitro and in vivo pharmacological properties of HR- 770 in neuroblastoma cells and confirm that HR-770 novel mechanism of action can favorably modulate pro-differentiation and cytotoxic pathways in several neuroblastoma cellular tumor models. The work performed under this proposal will generate critical data to assess the feasibility and merit of further pre-clinical development. Specifically, we will: 1) develop structure-activity relationships around HR-770 and characterize the potency and specificity of these compounds for each target pathway through a series of in vitro and cellular assays; 2) examine the in vitro and in vivo pharmacokinetic (PK) properties of HR-770 and top analogs; and 3) execute proof-of-concept studies in rodent models of neuroblastoma. Success in this proposal will lead to the submission of a Phase II grant focused on lead optimization and pre-clinical safety studies required for drug development candidate selection and subsequent IND-enabling studies.